1. Field of the Invention
The present invention relates to a reader adoptable in a copying machine for copying or duplicating an original document or the like or in other image forming apparatus such as facsimile. More particularly, the present invention relates a reader of the type in which the information bearing surface of original is optically scanned relatively and the color informations on the surface are discriminated for reading.
2. Description of the Prior Art
In the art there are known various types of readers which are adoptable in an image forming apparatus such as copying machine, facsimile etc. and which are used to read, for example, informations on an original document. One such readers is of the type in which an original table on which the information bearing surface is placed or movable elements constituting a reading optical system is reciprocated for reading the necessary information when it is wished to make two or more copies from an original.
In this type of known reader, reading is carried out only during the time of the movable member being moved forward and no reading is performed during the backward movement thereof. Therefore, the time required to read the original surface one time is essentially equal to the time required to complete one reciprocating motion of the movable member. It is obvious that this means a time consuming operation. To eliminate this disadvantage and to improve the reading efficiency, it has been proposed to increase up the speed of the backward movement as much as possible.
However, this known solution involves some problems. The mechanism for driving the movable member becomes very complicated. In addition, since the movable member is moved backward at a higher speed, means are required for absorbing the large shock generated when the moving member is stopped. This requirement also makes the stopping mechanism complicated.
As an important solution to the above problems, in the art, for example, in the art of electrophotography, there has been proposed so-called reciprocation reading process according to which the original surface is scanned not only during the forward movement of the movable member but also during the time of its backward movement. This is realized by interposing a Dachprism (roof prism) or a Dach-mirror in the optical path for projecting the light image of original onto a photoreception surface.
This known solution also involves some disadvantages. In the former case, one or two Dachprisms are required. The use of Dachprism brings forth the disadvantage of large loss of light. In addition, a particular mechanism is required to move the prism(s). Further, the positional relation thereof has to be changed for the forward movement and for the backward movement which also requires an additional change-over mechanism. After all, the driving part of the apparatus is very much complicated. This is the same in the latter case wherein Dach-mirror is used.
At present, there is an increasing tendency toward miniaturization of apparatus. Many efforts made in the art for this purpose have shown the need of reducing the optical path length itself. The above mentioned solution needs one or two Dachprisms or Dach-mirrors disposed in the optical path. Obviously, this is against the purpose of miniaturization and therefore not preferable.
As another development of a recording system there is known such type of novel image forming apparatus in which informations on an original are read in terms of bit units by self-scanning type photoreceptor elements or the like to transform the informations into electrical signals and recording is carried out digitally relying upon the electrical signals. One example of these novel recording systems an ink jet recording system.
If multicolor recording is wished with the ink jet recording system, two or more recording heads must be used. This is because with one and single recording head, the desired multicolor recording is hardly attainable in view of difficulty involved in ink supply. Generally, it is required to provide a plural number of heads equal to the number of colors to be used at that time for recording. For example, when recording is to be performed in two colors, red an black, two recording heads are usually required one for red and the other for black. In this connection, it should be noted that these two sets of heads are not allowed to be close to each other in arrangement. Some space must be provided between them for maintenance and also because of volume of head itself. Such space is necessary also for preventing the mixture of colors which may be caused by blotting of red and black inks on a recording paper at the time of printing. Furthermore, the time required to dry one of the color inks necessitates a certain interhead distance corresponding to the time.
Since the recording heads are disposed spaced from each other for the reasons mentioned above, reading of information must be made at two different points on the original simultaneously. The distance between the two points on the original corresponds to that between the two recording heads. Thus, when recording is carried out while driving both of the red and black recording heads simultaneously, reading and recording have to be carried out regarding information not at the same position on an original but at two different positions. The reading signals obtained at the two different points must be transmitted to the recording heads to effect multicolor recording.
To read a color original in terms of bit units and discriminate the color thereof between red and black, various known discriminating methods may be employed. According to one typical method, there is used a color separation system such as a beam splitter. A point on an original is divided into particular spectral wavelength regions by a beam splitter and then intensity of the spectral wavelength is detected by photoreceptor elements for every divided spectral wavelength region to discriminate one color from another.
Employing the prior art techniques relating to the ink jet head and color separation system described above, dichromatic recording can be realized by using two color separation systems for reading two points (two lines) on an original spaced from each other with a distance corresponding to the distance between two recording heads. However, this method requires four photoreceptor elements (2.times.2). Therefore, a larger space is required to receive the photoreceptor elements and also a complicated circuit is required to drive the elements. These are important disadvantages of the chromatic recording method.